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1.� -led <br /> San Joaquin County <br /> Environmental Health Department DIRECTOR <br /> �o•'_� . cp � Donna Heran, REHS <br /> Z: ? 600 East Main Street <br /> PROGRAM COORDINATORS <br /> Stockton California 95202-3029 <br /> � Robert McClellon, REHS <br /> .• Jeff Carruesco,REHS,RDI <br /> - P Website: www.s /ehd Kasey Foley,REHS <br /> 9� F p•R� �gov.or g Linda Turkatte,REHS <br /> Phone: (209) 468-3420 <br /> Fax: (209)464-0138 <br /> June 14, 2011 <br /> Mr. Weldon Church <br /> 1958 Yosemite Road <br /> Berkeley, California 94707 <br /> Subject: Weldon Church Property <br /> 104 West Beverly Place <br /> Tracy, California 95376 <br /> Dear Mr. Church: <br /> The San Joaquin County Environmental Health Department (EHD) has reviewed Site <br /> Conceptual Model and Human Health Risk Assessment Report (report), dated 06 April <br /> 2011, submitted by your consulting firm, Advanced GeoEnvironmental, Inc. (AGE) on your <br /> behalf for the above-referenced site. By letter dated 14 January 2011, the EHD had <br /> directed the submittal of a Human Health Risk Assessment (HHRA) and a Site Conceptual <br /> Model (SCM) and that additional soil gas samples be collected from the five temporary soil <br /> vapor sampling points, V-1 through V-5. <br /> In the SCM of the report, AGE describes the subsurface lithology and the migration <br /> pathways of petroleum hydrocarbon contamination released from the former 550-gallon fuel <br /> underground storage tank system. AGE estimates the mass of adsorbed total petroleum <br /> hydrocarbons quantified as gasoline (TPH-g) to be approximately 2,650 pounds and the <br /> mass of dissolved TPH-g to be approximately 4.88 pounds. The mass of dissolved benzene <br /> remaining in groundwater is estimated to be approximately 0.17 pounds. <br /> In the HHRA of the report, AGE presents the Tier 2 results obtained by entering the average <br /> concentration of benzene [85 micrograms per cubic meter (pg/m3)] detected in soil vapor <br /> samples V-1 through V-3 into the Johnson and Ettinger Model. The model calculated the <br /> cancer risk and hazard index as 7.42E-07 and 3.731 E-02, respectively. <br /> The EHD has concerns regarding how the data were employed to interpret the health risk <br /> posed through vapor intrusion. The EHD can find no authoritative guidance document that <br /> supports using the average soil gas concentration to calculate the cancer risk and hazard <br /> index. The Interim Final— Guidance for the Evaluation and Mitigation of Subsurface Vapor <br /> Intrusion to Indoor Air(guidance document), dated 15 December 2004 (revised 07 February <br /> 2005) published by the Department of Toxic Substances Control (DTSC), California <br />